The present invention is related to data storage, and more particularly to a data storage method and apparatus incorporating phase and amplitude modulation techniques to increase data storage capacity.
Increasing storage capabilities of a data storage medium while reducing the medium""s size has been an ongoing challenge in the industry. The industry has addressed these issues by increasing the data densities of existing storage media.
The theoretical storage capacity limits for existing disk drives depends on how closely the disk can reliably store adjacent symbols. If too many symbols are stored in a limited space, they will start to interact and exhibit intersymbol interference, making it impossible to recover the data corresponding to the interfering symbols. Existing research has focused on finding media that inhibit intersymbol interference or allow bits to be packed more closely together before the effects of intersymbol interference cause the data to be unrecoverable.
Conventional data storage methods divide the medium into individual cells that represent one bit each and either reverse or maintain the magnetization direction of each cell. In double-frequency modulation, for example, a xe2x80x9c1xe2x80x9d is represented by a reversal of magnetization in a cell and a xe2x80x9c0xe2x80x9d is represented by the absence of a reversal. Viewed another way, the signal from the medium can be analyzed such that a phase shift of 180 degrees represents a xe2x80x9c1xe2x80x9d and the absence of a phase shift represents a xe2x80x9c0xe2x80x9d.
Because each data symbol is represented only by one bit, the amount of data that can be stored on the hard drive is limited.
There is a need for a data storage method and system that increases the storage capacity of a magnetic based data storage system while inhibiting intersymbol interference caused by storing symbols too closely together.
Accordingly, the present invention is directed to an apparatus for writing data to a medium that can store a plurality of symbols, comprising: a data encoder that receives serial data as an input and converts the serial data to parallel data, a modulator that receives the parallel data from the data encoder, and a write head responsive to the modulator for writing at least two bits per symbol on the medium based on the parallel data.
The present invention is also directed to an apparatus for reading data from a medium having a plurality of symbols, wherein at least one of the symbols contains at least two bits per symbol, comprising: a read head that reads the symbols from the medium, a demodulator that converts the symbols into parallel data, and a data decoder that receives the parallel data as an input and converts the parallel data to serial data.
The invention is further directed to a method for writing data to a medium, comprising the acts of: converting serial data to parallel data and writing at least two bits per symbol on the medium based on the parallel data.
Additionally, the invention is directed to a method for reading data from a medium having a plurality of symbols, wherein at least a portion of the symbols contain at least two bits per symbol, comprising the acts of: reading the symbols from the medium, converting the symbols into parallel and converting the parallel data to serial data.